LEDs are electronic devices that require specific equipment and system designs to ensure that high lumen output and long life are attained and maintained. To ensure specification integrity, a lighting system is typically tested using a viable test methodology. The Illuminating Engineering Society of North America (“IESNA”) has developed the “LM79-08 Approved Method: Electrical and Photometric Measurements of Solid-State Lighting (SSL) Products” (“LM79”) to standardize this methodology. LM79 test data allows an end user to evaluate the suitability of the SSL system, such as a lighting fixture, for its use in a particular application or to compare SSL systems with one another. LM79 provides data for total luminous flux, electrical power, and efficacy and chromaticity.
The IESNA has also developed the “LM80-08 Approved Method for Measuring Lumen Maintenance of LED Light Sources” (“LM80”) to cover lumen maintenance measurement for LED packages, arrays, and modules. LM80 sets the standards for uniform test methods for LED manufacturers, which measure LED lumen maintenance. The LED lumen maintenance is measured while controlling case temperature of the LED, forward voltage to the LED, and forward current to the LED. The LM80 standard also requires lumen maintenance data for at least 6,000 hours of constant DC mode operation.
As such, test results based on the LM79 and LM80 standards provide an accurate estimate of lumen depreciation in a LED lighting system. LEDs are replaced based on the lumen depreciation. The Illuminating Engineering Society (IES) recommends that the LEDs (or any other light source) should be replaced when the light output degrades to about 70% of the initial light output.